Loudspeaker and method of making the same



Oct. 10, .1939. P. A 2,175,994

LOUDSPEAKER AND METHOD OF MAKING THE SAME Filed June 25, 1938 Patented Oct. 10, 1939 UNITE STATES LOUDSPEAKER AND METHOD OF MAKING I v THE SAME James P. Qnam, Chicago, 'Ill., assignor to quam Nichols Company, Chicago, 111., a corporation of Missouri Application June 23, 1938, Serial No. 215,484

7 Claims.

My invention relates in general to loudspeakers and more in particular to a dynamic-type loudspeaker employing a hollow but substantially entirely closed permanent magnet structure, and

5 to a method for manufacturing a loudspeaker of this type and general construction.

In the manufacture of permanent magnet dynamic-type speakers wherein the permanent magnet is of a box-like construction which is 10 hollow and substantially closed, a great 'deal of difllculty has been encountered in cleaning out metal particles, core sand, and similar foreign matter from the permanent magnet cavity. As a result, such undesired matter often lodges in 15 the voice coil aperture after the complete assembly of the speaker in a manner to'impede or dis-' forts have been made to dislodge and remove such accumulation of foreign matter from within the 20 cavity inthe permanent magnet by means of a blast of compressed air, or by means of air suc .tion applied at the voice coil aperture. Such cleaning methods, however, usually result in only a partial removal 01'. the foreign matter because 26 some of the metal and dirt particles, and the like, merely whirl around in the cavity, and particularly in the corners thereof, while the pressure is on, but settle back into the cavity when the pressure is removed. The metal or dirtparticles which are not removed from the permanent magnet cavity normally subsequently fall into'the voice coil aperture or become lodged therein during the final assembly operations and testing of the speakers in the factory, or after 35 the speakers have been installed in a receiver and have gone into service. Such particles in the voice coil aperture interfere with or stop the movement of the voice coil in its air 'gap, and normally the voice coiland diaphragm have to 40 be removed before the particles can be removed.

. A new diaphragm and voice coil have to be substituted because the original members are torn in removing. This is very costly when it has to be done in the factory, and much more costly 45 when the, troublebecomes apparent out in the field.

viding a relatively large-air gap at the-voice coil aperture. This is extremely undesirable, how- 50 ever, because the larger the'air gap the sinaller the magnetic forces at the aiij gap, and hence the weakerthe magnetic'forcefavailable for moving the voicegcoil in such" air gap. It is understood, of course, that the ideal construction for 55 a speaker from, the standpoint of operation intort the movement of the voice 'coil therein. Ef-

Someof these dimculties' are overcome by proplate of the magnet forming the air gap. How-' ever, with such a small air gap the danger of interference arises from even the smallest foreign particles.

It is an object of. my invention to provide an improved dynamic-loudspeaker employing a substantially closed but hollow permanent magnet.

A further object of my invention is to provide a method for the manufacture of speakers of the above described construction so that metal and dirt particles and similarforeigmmatter can be eflectively removed from the permanent magnet structure after the assembly thereof, or if not entirely removed, can be positively sealed onto the inside wall of the permanent magnet so that it cannot become dislodged to fall or be attracted into the voice coil air gap in the permanent magnet.

It is also an object of my invention to produce better speakers of this general construction at a materially lower cost.

A still further object oi. my invention is to provide a speaker of the construction described having a voice coil efiectively operating in a relatively small voice coil aperture or air gap.

Another object is to provide a method for washing metal and dirt particlesfrom a substantially closed, hollow space in a manufactured article and simultaneously sealing any such particle which are not removed, onto the wall of such hollow space.

Other objects and advantages of my invention will be apparent from the following description,

. taken with the drawing, in which:

Fig. 1 is a cross-sectional view of a portion of the complete permanent magnet for the loudspeaker in one of the preliminary stages of assembly.

Fig. 2 is a similar view of the permanent magnet structure in a subsequent step in the process of manufacture. I

Fig. 3 is a cross-sectional view of the speaker with the metallic portions assembled, and illustrating a subsequent step in the process of manufacture of the speaker.

Fig. 4 is a' cross-sectional view of a complete speaker embodying my invention and completed in accordance with the method of ,my invention.

In practici-ngmy invention, an annular magnetportion I0 is provided with a pair of end plates llfand l2 welded thereto to'provide a box- 56 moved by blowing or the like.

corresponding aperture IS in the end plate H with a rigid driving fit. The core I may be assembled onto thelend plate II in an appropriate jig before the end plate II is assembled onto the ring III, or the end plates II and I2 may be originally assembled on the ring as described above, and the core then driven into the aper-. ture 16 while being centered in the voice coil aperture l3 of the plate If.

A stamped-out diaphragm frame I! known as a basket in the art, is centered with respect to the voice coil aperture l3 and then welded to the outside face F of the plate l2. This latter assembly can likewise be accomplished in either one of two different orders, viz., the basket i! may be first welded to the plate I! and then the latter with the basket thereon, welded to the annular ring In, or as previously mentioned, the basket may be welded to the plate I? after the latter has been welded to the annular ring ID.

The elements of this preassembly, viz., the annular ring III, the end plates II and H, the core l4, and the basket ll, are all cast, stampedout, or machined members, and the original production of the same, (except, of course, the casting of the ring ID) as well as the welded assembly thereof is normally accomplished in the machine shop portion of the factory. As a result, there is normally some core sand, slivers of steel, and other metal and dirt particles, on the preassembly and within the magnet cavity represented by the reference character C inFig. 2. In this connection it is understood. of course, that other configurations for the permanent magnet may be provided resulting in a box-likestructure with an internal cavity, all within the .concept of the present invention. As stated above, the generally accepted procedure in the manufacture of loudspeakers of this general construction prior to my invention was to direct a stream of compressed air from a high-pressure nozzle into the cavity C through the voice coil aperture l3 after the preassembly to the extent illustratedin Fig. 4 has been completed, or apply a suction at the aperture. However, as further explained, this has been insuflicient to remove all foreign material from the cavity, and as a result a goodly number of speakers have had to be torn down after assembly, removing the diaphragm and voice -coil so that particles which had become lodged in the voice coil aperture could be reagainst failure in the field, because some of the material which lodged in the voice coil aperture might be blown back into the cavity C again, escape detection in the fac tory'andthen drop into the voice coil aperture after the speaker had been put into use.

These difiiculties have been substantially completely eliminated in the commercial practice of my invention which includes providing a drain opening l8 at one side of the end plate H in such a position that it will be coextensive with the inside surface of the annular ring ill as shown clearly in Figs. 1, 2 and 3, inclusive. After the assembly of the magnet structure and the diaphragm frame I! as described above, and with the drain it open, theentire unit is dipped into a paint tank. The paint completely covers the outside of the unit and flows into the cavity a complete insurance C through the voice coil aperture, and the are effectively carried 7 machine shop Even this was not there might be in the drain opening l8 until the cavity C is entirely filled. This operation, of course, requires only a second or two. The unit as illustrated in Fig. 3 is then suspended from a rack or the like over a suitable drain pan in a position such that the opening I8 is at the lowest point in the cavity C so that the paint in the cavity will drain out completely. Relatively light paint is preferably employed, aluminum paint being quite satisfactory, and this flows readily out of the voice coil aperture l3, into the cavity C, and out of such cavity through the opening it, so that only a very thin film of paint remains over the entire structure. With the unit suspended as shown in Fig. 3, the last drop of paint, in draining, ac-

cumulates and dries, if at all, at the drain opening I8. This does not affect the operation of the speaker in any manner, and with the paint draining in the direction noted, the film at the voice coil aperture I3 is so thin that it will not impede the movement of the voice coil therein even though the air gap intermediate the pole piece and aperture wall is very narrow.

As the paint drains from the inside of the cavity C, the -objectionable (with the paint and removed from the unit. If any such particles remain, these are sealed onto the surface of the magnet, inside and out, during the drying operation so that they cannot fall into the air gap at the voice coil aperture l3 to cause trouble. Thethin film of paint is illustrated on the magnet in Figs. 3 and 4 at the cross-section portion as a narrow border over the entire inside of the cavity C, the voice coil aperture l3, and over the outside of the magnet structure. The border,v of course, does not indicate the thickness of the coating on the unit. The paint also covers the basket I1. After the paint has drained from the preassembled unit, the unit is placed in a baking oven at approximately 450 F., and dried for approximately thirty minutes. The time and temperature for the drying, of course, will vary with the paint used for the cleaning and sealing operation. After the drying operation, a hard clean surface is provided over the entire. magnet structure and basket.

The painting and drying steps are normally carried on in a paint shop separate from the wherein the original assembly is completed, and after the drying operation, the painted unit is carried directly to the assembly lines which are normally comparatively free from dust and metal particles. In the assembly line the diaphragm l9 and voice coil 2i, shown in dotted lines in Fig. 4, are mounted upon the basket I! with the voice coil centered in the air gap at the voice coil aperture l3.- The speaker is then substantially complete, and as a final precaution an air blast is applied to the aperture l8 which is still open and any slight dust that voice coil aperture I8 is blown outwardly from the magnet structure. A metal plug 22 of soft material is then forced into the aperture '18 with a suitable punch and the cavity 0 is sealed completely except, of course, for the voice coil aperture I). The magnets are then magnetized, and the speakers tested and made ready for shipment.

In the commercial practice of this invention,

it has been found that rejects due to the accumulation of foreign matter in the voice coil aperture, and the failure of speakers in the field due to this cause have been reduced substantially to nothing. In addition to thus materially remetal and dirt particles ducing the cost of production, the practice of my invention has made possible an improved speaker of dynamic type utilizing an enclosed permanent magnet. This improvement has resulted from a smaller voice coil aperture made possible by freedom from dirt and the like, and in addition the magnet structure of the speaker is protected on the inside and.out against corrosion, rust, or the like, due to a. moisture accumulation thereon.

Although I have described my invention in its preferred embodiment, it is understood that the invention is not limited thereto, but changes and modifications may be made therein, all within the scope of the appended claims.

I claim:

1. The method of producing a field magnet for a loudspeaker adapted to have a voice coil moving in an air gap in said magnet and protecting said air gap "against the introduction therein of metal and dust particles from the inside of the magnet so as to interfere with the movement of the voice coil in said air gap;

which method comprises assembling a multipiece magnet in a manner to provide a hollow cavity therein with said magnet having an annular opening in one side thereof to provide a voice coil air gap and having an edge aperture in an Opposite side, substantially filling said magnet cavity with a liquid, draining said liquid from said cavity at said edge aperture to thereby wash metal and dust particles from within said cavity through said aperture, baking said magnet to dry a covering of said liquid on the inside wall of said cavity to seal any remaining metal and dust particles thereon, and plugging said edge aperture to substantially close said magnet over the entire body thereof except for said annular opening.

2. In a field magnet for a loudspeaker, said field magnet being hollow walled forming a substantially inaccessible cavity having an air gap in one wall of'said magnetand an opening in a ,wall other than the air gap wall, a method for preventing normally loose particles within the substantially inaccessible cavity from entering the air gap in said field magnet, which method includes substantially filling said cavity of said magnet with a'liquid, draining said liquid from said cavity through said wall opening to wash said particles from within the cavity and carry the same with the liquid through said opening, and drying the liquid on the inside walls of the cavity to thereby seal any remaining particles within the cavity onto said inside walls in a manner to prevent such particles from entering said air, gap.

3. A method for removing loose particles of undesired material from within a substantially closed hollow permanent magnet housing having a substantially inaccessible cavity therein and sealing any remaining particles to the inside wall of said cavity, with said housinghavin'g at least two diiferent openings out of said cavity with each opening in a different wall of the housing, which method includes immersing said housing in a liquid bath for a time suflicient tosubstantially fill the inside of said housing. draining said liquid from one of said openings to wash undesired loose particles from said cavity and carry said particles with said draining liquid, subjecting said housing to a temperature for drying a film of said liquid onto the inside walls of said cavity to retain any remaining loose particles therein and seal said particles onto said walls, and thereafter closing the opening from which the liquid drained.

4. The method of manufacturing a loudspeaker.

having a walled magnet unit of magnetic material with a voice coil air gap in one wall, a cavity within said walls substantially closed thereby except for said voice coil air gap and a drain opening from said cavity, which method includes the steps of substantially filling said .cavity with a liquid, draining said liquid from said cavity through said drain opening to wash particles within the cavitytherewith and leaving only a coating of said liquid within said cavity on the walls thereof with any remaining particles carried in the coating, and drying the coating on said cavity walls to seal said remaining particles therein. and prevent such particles from entering the voice coil air gap.

5. The method of manufacturing a loudspeaker having a walled magnet unit of magnetic mauid from the cavity through said drain opening to wash particles within the cavity therewith during said draining and leaving only a coating of said liquid within said cavity on the walls thereof with any remaining particles carried in the coating, drying the coating on said cavity walls to seal said remaining particles therein and prevent such particles from entering the voice coil air gap, and closing the drain opening. 6. In a loudspeaker having a diaphragm thereon, a walled permanent magnet having an air gap in one wall thereof and having an internal cavity formed by said walls and substantially closed on all sides except for said air gap, and a dry coating of sealing material on the walls of said internal cavity to seal undesired particles therein and prevent said particles from entering into said air gap.

'7. In a loudspeaker having a diaphragm, a voice coil secured to said diaphragm, and a diaphragm frame, a magnet unit having walls of magnetic material with a voice coil aperture in one wall, with said walls forming an internal cavity within the unit substantiallyclosed except for the voice coil aperture, a dry covering over the walls of said internal cavity for re taining normally loose particles and preventing such particles from entering said air gap from a point within said cavity, with one of the cavity walls having an opening-therein, and a plug in said opening.

- JAMES P. QUAM. 

